The invention concerns a pipe adapter, with an insertion stub for the pipe end to be connected and provided with an inner cone to receive a correspondingly shaped outer cone at one end (press end) of a sealing bush slipped on the pipe end, the other end (cutting end) of this bush being provided with a further outer cone which is overlapped by the correspondingly shaped inner cone of a clamping ring and with at least one cutting edge on the inside of the sealing bush and running circumferentially against the outer wall of the pipe end, while the inside of the outer cone of the press end is cylindrical, the cone angle of the cutting end being larger than that of the press end.
In a known system of this type as disclosed in West German published application No. 30 25 292 or British patent No. 20 54 078, both corresponding to U.S. Pat. No. 4,309,050, the sealing bush consists of two parts, the press end being a somewhat softer material which plastically deforms under high pressure.
This system suffers from the drawback that such deforming materials lack elastic properties, whereby sealing cannot be assured permanently. Moreover the relative small cone angle of the cutting end prevents substantial axial forces from being applied to the press end for the purpose of achieving adequate sealing that would result from the consequent higher compression. This feature is aggravated in the known system of Legris because the sealing bush is provided with a stop surface extending in a plane perpendicular to the pipe axis and therefore rests against a corresponding surface of the insertion stub and hence prevents substantial compressive forces from being applied.
Lastly the known system incurs the drawback that an additional component is required for sealing, entailing thereby higher expenditures both in manufacture and assembly.
Pipe adapters are known from West German published application No. 14 50 382 where the press end and the cutting end of the sealing bush are combined by the inwardly pointing cutting edges located on the inside of the press end.
However it has been ascertained that both designs are unsuitable for pipe systems moving corrosive media, for instance acid gases containing H.sub.2 S, because in spite of the use of corrosion-resistant materials for the piping, both the pipe material and the sleeve material will corrode due to the reactivity of the medium, because the zone of maximum stress concentration, that is especially the cutting surfaces and the surface in the pipe material associated with them are located in the area of maximum exposure to the corrosive medium, resulting in stress crack corrosion and therefore leakage. The known design entails a further drawback for the cited application in that the sealing bushes are gas-nitrided at least in the vicinity of the cutting edges to achieve adequate surface hardness, whereby they lose at their surface their originally corrosion-resistant properties. Because such pipe adapters perforce will leak after some time in operation in the cited applications, the moved corrosive media, for instance acid gases, being damaging to health when not downright poisonous, pipe adapters of the known types must be constantly checked for tightness if they are used at all in such applications.